Long before we have watches, people have always tell time by Sun Dials. Mechanical watches did not become generally available until early 20-century. The designers of these watches natually make the hands of their watch to emulate the movement of the shadow of a sun dial.Plant a 8-ft long post on the ground. This pole is called the "gnomon" of the Sundial. Stand in front of it facing North. Watch the shadow cast by the Sun on the ground. It looks like this.
Is it any wonder that when the watchmakers began to make watches to compete with sun dials they make the hands of their clocks rotating clockwise as well? Just like the Sun Dial!
NASA has a webpage showing this fact as well as a lot of additional details. bri